In contests, knowing which font to use is an advantage. Fonts can influence the outcome of an entry so remarkably that they may even become the deciding factor.
Which fonts should I use?
The best way to find out is to check the contest’s brief or description. Visit the contest page and have a look at what the contest holder wrote. If they have a strong vision and specific instructions, it is likely that they already have a font or two in mind. If you feel like you can improve on these choices, message your suggestions to the contest holder through the Public Clarification Board, and if permitted, you can then submit more than one entry with varying fonts.
If there are no guidelines, you can unleash your creativity. Just make sure that you legally acquire the fonts you plan on using by securing the necessary licenses or rights. If not, you risk your entries getting rejected or reported.